https://www.youtube.com/watch?v=cL6S5TeHbAc
in their it's never too late AQ guide posted yesterday it clearly shows Map 7's cost.
Just so you don't have to watch the Agony of it, mind you there are several errors in their tips guide, the cost for the MYTHIC Difficulty with a 20x multiplier is:
750,000
50,000
125,000
Which is the same Cost as 6.
It still could be a developmental and subject to change, but it looks like the changes haven't been reflected yet in their testing environment.